I have bitten my nails for over 20 years. In fact I have bitten them for as long as I can remember. And I don't mean I bit them to trim them. It was worse than that. Talk about a habit.
I have not bitten my nails in almost 3 months. I think I can safely say, I have finally kicked the habit. My primary motivation for wanting to stop was that I didn't want either of my daughters to copy me. The funny thing is, I've been motivated before but never succeeded. Not for very long anyway.
Have a 2 year old and an infant to keep you busy from waking to collapsing. LOL. Worked for me.